The United States Secret Service (USSS or Secret Service) is a federal law enforcement agency under the Department of Homeland Security with the purpose of conducting investigations into currency and financial-payment crime, and protecting U.S. political leaders, their families, and visiting heads of state or government.[3] The Secret Service was, until 2003, part of the Department of the Treasury, due to their initial mandate of combatting counterfeiting of U.S. currency.[4] The agency has protected U.S. presidents and presidential candidates since 1901.[5]